High-Quality BIMA-OVRO Images of Saturn and its Rings at 1.3 and 3 Millimeters

We present high-quality data of Saturn and its ring system from the Berkeley-Illinois-Maryland Association and Owens Valley Radio Observatory arrays. We observed at wavelengths of 1.3 and 3.0 mm in 2002 October and 2003 March, respectively. At that time Saturn's rings were near their maximum ring opening angle (|B| ∼ 26°), which allowed us to map the brightness distribution on Saturn's disk, as well as from its rings, despite the moderate resolution achieved (∼2.″5–4″). Clear latitudinal structure is seen on Saturn's disk, indicative of an overall upwelling of gas on the southern hemisphere and subsidence of dry air in the north. The rings are brighter at 1.3 mm than at 3.0 mm, as expected from the increase in ring particles' thermal emission at shorter wavelengths. We use our radiative transfer code to model the relative contributions of the scattered and thermal radiation emanating from the rings. Unlike previous (centimetric) observations, the present (millimetric) data serve as an adequate test of the model's ability to account for the thermal contribution from the rings. A comparison between the model and data shows that Saturn's light transmitted and scattered through the B ring, as well as the radiation reflected from the A ring behind and just off the planet's south pole, is much brighter than predicted by our model. Hence, the ring particles appear to scatter more efficiently both in the forward and backward directions than implied by an isotropic phase function.

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